In contrast to the conventional light-emitting apparatuses such as incandescent lamps or fluorescent lamps, electron-beam excitation type light-emitting apparatuses have recently been developed which call for the electrons emitted in a vacuum chamber from an electron emission source to be thrown at high speed upon a fluorescent material thereby causing the fluorescent material to emit light upon excitation therewith for use in illumination or image display.
This type of light-emitting apparatus, as for example disclosed in Japanese Unexamined Patent Application Publication No. 2004-207066 (Patent reference 1), is generally structured to pass the emitted light from the surface of the fluorescent material through a glass substrate at the back side of the fluorescent material and to radiate it exteriorly; however, with this structure, even though the side of the fluorescent material irradiated with the electron beam generates the most intense light emission, that emitted light ends up dissipating as a useless light emission in the vacuum chamber, so that it cannot necessarily be said that the light emission efficiency of the apparatus is good.
For this reason, a technology is known for electron beam excitation type display devices, which calls for forming a metal back layer by vapor deposition of aluminum or the like on the side of the fluorescent material which is irradiated with the electron beam, thereby enhancing the brightness. Metal backs are designed, in addition to specularly reflecting the light to the device interior side from the fluorescent material to a device exterior side (a display face side or illumination face side), thereby enhancing the brightness, to protect the fluorescent material from damage by electrons charged on the fluorescent face, damage by impingement of negative ions generated within the device, and the like, which is, for example, disclosed in Japanese Unexamined Patent Application Publication No. 2000-251797 (Patent reference 2).
The technology of Patent reference 2 comprises, in an image generation device for displaying an image by causing a fluorescent film to exhibit light, dividing a metal back provided in the interior face side of the fluorescent film into multiple portions and covering the multiple gaps dividing these portions with a conductive material, thereby preventing a creeping surface discharge from the surfaces of the gap portions due to an abnormal electrical discharge generated in a vacuum and attaining the stabilization of display quality.
However, the technology of improving the device's light emission efficiency using a metal back is such that upon the electron beam penetrating the metal back layer, the acceleration energy thereof is lost, thereby lowering the fluorescent material's excitation efficiency. In particular, for applications in illumination devices, a decrease in fluorescent material's excitation efficiency resulting from the loss of its acceleration energy can neither be ignored nor is conducive to a fundamental improvement in light emission efficiency.
To address this problem, Japanese Unexamined Patent Application Publication No. H10-12164 (Patent reference 3) discloses a technology on a thin display device, comprising a cathode plate which is provided with an emitter electrode line equipped with emitter tips in domains constituting pixels and a gate electrode line mounted so as to intersect the emitter electrode line in the domains constituting pixels, and an anode electrode plate having a fluorescent material layer, which are mounted oppositely with a predetermined separation, wherein at least the domains of the emitter electrode line and gate electrode line that constitute pixels are composed of transparent electrode films, whereby one can observe the emitted light of the fluorescent material layer through the two transparent electrode films, that is, to watch the emitted light of the fluorescent material from the fluorescent material's surface side.
The display technology of Patent reference 3, when used as a display device, can provide a high brightness display by viewing the emitted light from the fluorescent material's surface side; but when contemplated for an illumination application, this would mean acquiring illumination light through the cathode plate opposing the fluorescent material layer. In other words, this would end up using, as illumination light, the light released exteriorly through the gaps between the emitter tips and the lower layer metal conductive films of the emitter electrode line and gate electrode line; accordingly the light radiated from the fluorescent material would decay or scatter, preventing an effective use of the emitted light from the entire face of the fluorescent material.
The present invention has been made in view of the above-mentioned situation, and its objective is to provide a light-emitting apparatus which is capable of causing the light emitted at the entire face of a fluorescent material to be emitted exteriorly with no interference and with enhanced light emission efficiency, thereby attaining an exteriorly radiated high brightness light.